This invention relates generally to a method for agglomeration of flue gas desulfurization dust, and more particularly to a method for agglomeration of dry, free-flowing dusts containing calcium and sulfur such as those resulting from the flue gas scrubbing of combustion processes using calcium-based scrubber reagents. This invention further relates to the use of the agglomerated product as a soil additive.
Calcium-based scrubber reagents are being used to remove sulfur oxides (SO.sub.x) from the flue gases resulting from the combustion of carbonaceous, sulfur-bearing fuels of all types, such as coal burning power stations. A dry powder, aqueous suspension, or solution of the scrubber reagent is injected or atomized into the flue gas for the absorption of SO.sub.x producing a dry waste dust. The products of reaction of the calcium compounds in the scrubber reagent with the SO.sub.x in the flue gases include calcium sulfite (CaSO.sub.3) and calcium sulfate (CaSO.sub.4). These reaction products, unreacted calcium compounds, and flyash, along with other emissions, are generally removed in dust collectors such as electrostatic precipitators or fabric filter baghouses. The final composition of the dust thus removed depends on several factors including the composition of the flyash in the flue gas, the composition of the calcium-based scrubber reagent, and on the operation of the scrubber equipment.
Enormous amounts of flue gas desulfurization dust are produced annually nationwide, principally from the burning of coal in power plants. The collected dust is a very fine, powdery substance which leads to storage and handling problems because it is difficult to confine to a desired area. Disposal of flue gas desulfurization dust poses an increasingly difficult problem because the volume, powder-like nature and varied chemical composition of the dust limit the number of acceptable disposal options. Furthermore, the capacity of acceptable disposal sites is not unlimited. Moreover, calcium sulfite is a relatively insoluble salt and a high calcium sulfite content in the dust may cause some restrictions as to the disposal or industrial utilization of the dust.
The use of calcium and sulfur as soil additives is well known. However, many of the forms in which calcium and sulfur can be added to the soil, such as calcium sulfite, are relatively insoluble. Furthermore, calcium sulfite typically exhibits thixotropic properties and does not readily lend itself to agglomeration. Therefore, flue gas desulfurization dust has heretofore had limited agricultural applicability.
For reasons such as the foregoing, there is a need for a method for economically rendering the dust produced by flue gas desulfurization systems into a free-flowing, handleable and useful product rather than merely discarding it. Ideally, the product would have agricultural application as a soil additive. Thus, there is a need for an economical use of flue gas desulfurization dust from the calcium-based scrubbing of combustion flue gases.